1. Technical Field
Exemplary aspects of the present invention generally relate to a liquid ejection head and an image forming apparatus including the liquid ejection head.
2. Related Art
Like a printer, copier, plotter, facsimile machine, or multifunction device having two or more of these capabilities, an inkjet recording device employing a liquid ejection recording method is also a type of image forming apparatus.
Typically, the inkjet recording device includes a recording head constructed of a liquid ejection head that ejects droplets of a recording liquid such as ink onto a sheet of a recording medium to form an image on the sheet. The liquid ejection head has a nozzle face in which multiple nozzles, from which droplets are ejected, are formed. Ejection characteristics of the liquid ejection head, such as the volume and speed with which droplets are ejected from the nozzles, varies considerably depending on the shape and quality of each nozzle. It is also known that surface characteristics of a nozzle substrate, in which nozzle holes each forming the nozzle are formed, also considerably affects the ejection characteristics of the liquid ejection head. For example, adhesion of ink or the like to the area around the nozzle on the surface of the nozzle substrate may distort the trajectory of the droplets ejected from the nozzle.
To solve these problems, a liquid-repellent film is often formed on the surface of the nozzle substrate on a side from which droplets are ejected (hereinafter referred to as a droplet ejection side). As a result, the droplet ejection side of the nozzle substrate has a uniform surface across the surface of the nozzle substrate, thereby stabilizing the ejection characteristics of the liquid ejection head.
To further stabilize the ejection characteristics of the liquid ejection head, the nozzle face of the liquid ejection head is often wiped off and cleaned by an elastic blade such as a wiper formed of rubber or the like to remove liquid adhering to the portion around the nozzle during maintenance of the liquid ejection head.
However, repeated wiping of the nozzle face of the liquid ejection head abrades and wears away the liquid-repellent film around the nozzles, causing irregular ejection of the droplets from the liquid ejection head. In particular, because the wiper hits the edge of each nozzle relatively hard, the liquid-repellent film at the edge of the nozzle is easily abraded and worn away by such wiping.
To solve these problems, a concavity is often formed around the nozzle in the nozzle substrate on the droplet ejection side. However, formation of the concavity generates a step in the nozzle face, and an edge of the step is subjected to excessive load from the wiper that contacts the step, resulting in abrasion and wearing away of the liquid-repellent film at the step. In addition, it is difficult to remove viscous liquid accumulating within the concavity.
The concavity formed around the nozzle in the droplet ejection side of the nozzle substrate may be gradually tapered toward the bottom. However, although such a configuration reduces abrasion and wearing away of the liquid-repellent film at an outer circumferential part of the tapered concavity, the edge of the nozzle is still hit hard by the wiper. Consequently, durability of the liquid-repellent film at the edge of the nozzle deteriorates.
Alternatively, the thickness of the liquid-repellent film can be gradually reduced approaching the edge of each nozzle. However, such a configuration makes the liquid-repellent film excessively thin at the edge of each nozzle. Consequently, durability of the liquid-repellent film at the edge of the nozzle deteriorates, abetting abrasion and wearing away of the liquid-repellent film.